The present application relates to a micro-oscillator to be an element of devices such as a signal filter, mixer and resonator, a semiconductor device including the micro-oscillator and a communication apparatus that uses a band filter including the micro-oscillator.
A micro-oscillator produced by using micro-machine (MEMS: Micro Electro Mechanical Systems) technology is widely known. A use of this micro-oscillator as a high frequency filter has been proposed by research institutes including Michigan University (see, C.T.-Nguyen, Micromechanical components for miniaturized low-power communications (invited plenary), proceedings, 1999 IEEE MTT-S International Microwave Symposium RF MEMS Workshop, Jun. 18, 1999, pp 48-77).
FIG. 1 schematically shows a micro-oscillator constituting the above-described high frequency filter, that is, a beam-type oscillator with electrostatic drive. The oscillator 1 includes: an input-side wiring layer 4 and an output electrode 5 which are made of polycrystalline silicon, for example, and are formed on a semiconductor substrate 2 through an insulation film 3 and an electrode to be an oscillation plate, what is called a beam 7, formed to face this output electrode 5 across a space 6 to be an oscillating plate. The beam 7 is connected to the input-side wiring layer 4 by straddling like a bridge to be supported by anchor portions (support portions) 8 [8A, 8B] at both ends. The beam 7 functions as an input electrode. An input terminal t1 is led out from the input-side wiring layer 4 and an output terminal t2 is led out from the output electrode 5, respectively. In this oscillator 1, a high frequency signal Si is supplied to the beam 7 through the input terminal t1 in a state where a direct current bias (hereinafter, referred to as a DC bias) voltage V1 is applied between the beam and the ground. Specifically, when the DC bias voltage V1 and high frequency signal S1 are overlapped and supplied from the input terminal t1, the beam 7 having a natural oscillation frequency determined by the length, oscillates by an electrostatic force generated between the output electrode 5 and the beam 7. With this oscillation, a high frequency signal corresponding to a temporal change of capacitance between the output electrode 5 and the beam 7 and the DC bias voltage is output from the output electrode 5 (hence, from the output terminal t2). A signal corresponding to the natural oscillation frequency (characteristic frequency) of the beam 7 is output in the high frequency filter.
On the other hand, there has been no verification in which the structure of a DC power feeder line from an oscillator is studied from the standpoint of securing a signal strength when signal processing is performed, in the case where one or a number of oscillators are disposed on a semiconductor substrate or on a substrate such as an insulating substrate to perform signal processing.
FIG. 2 shows another structure of the above described electrostatic drive micro-oscillator as related art. The micro-oscillator 11 includes: an input electrode 14 and an output electrode 15 formed on a polycrystalline semiconductor substrate 12 through an insulation film 13 and an electrode to be an oscillating plate, that is, a beam 17 formed to face those input electrode 14 and output electrode 15 across a space 16. The beam 17 straddles the input electrode 14 and output electrode 15 like a bridge and is integrally supported by anchor portions (support portions) 19 [19A, 19B] at both ends to be connected to a wiring layer 18 disposed outside the input and output electrodes 14 and 15. An input terminal t1 is led out from the input electrode 14 and an output terminal t2 is led out from the output electrode 15. A required DC bias voltage V1 is applied to the beam 17.
In this micro-oscillator 11, when a high frequency signal S1 is input into the input electrode 14, the beam 17 resonates by electrostatic power generated between the beam 17 to which the DC bias voltage V1 is applied and the input electrode 14, and a high frequency signal of an objective frequency is output from the output electrode 15. According to the micro-oscillator 11, since the facing area of the input and output electrodes 14 and 15 can be small and an interval between the input and output electrodes 14 and 15 can be large, parasitic capacitance C11 between the input and output electrodes becomes small in comparison to the oscillator 1 of FIG. 1. Therefore, a signal directly transmitted through the parasitic capacitance C11 between the input and output electrodes 14 and 15, in other words, a noise component becomes small and an S/N ratio of an output signal can be improved.
On the other hand, as shown in FIG. 3, there has also been proposed the one in which a plurality of oscillators (hereinafter, referred to as oscillator elements), for example, oscillator elements 21 [21A, 21B, 21C] including input and output electrodes 14, 15 of lower electrodes and a beam 17 are provided on the same substrate as an oscillator group such that the input and output electrodes 14 and 15 are connected in parallel to be shared in common, and so combined impedance of the entirety decreases to be applied to a high frequency device.
Here, as described above, the electrostatic drive oscillator includes a beam capable of oscillating and an electrode, and the beam is electrically oscillated by the electrode disposed apart. The oscillation is excited in the vertical direction with respect to the substrate. In order to extract an electrical resonance signal from a mechanical resonance of the beam, DC bias voltage is required to be applied between the beam and the electrode. As a matter of course, the beam needs wiring, that is, a DC bias feeder wire to apply the DC bias voltage.
Further, as explained in FIG. 3, in order to reduce the impedance of the electrostatic drive resonator, oscillator elements have been provided in parallel. This is because it is more convenient from a manufacturing perspective to dispose in parallel a large number of oscillators of suitable size rather than to dispose one huge oscillator. The DC bias feeder wire between the oscillator elements becomes necessary when the oscillators provided in parallel.
However, although the impedance decreases when oscillator elements are provided in parallel, an area where the whole oscillator system is installed, specifically, the ground capacitance increases at the same time. With the leakage of a signal to the substrate side through ground floating capacitance connected to the path of the signal, loss of an output signal is caused.
Additional features and advantages are described herein, and will be apparent from, the following Detailed Description and the figures.